1. Field of the Invention
The invention relates to a method and apparatus for monitoring the production of plastic blow molded containers. More particularly, the invention contemplates the sensing of defects caused by the formation of holes in the walls of plastic blow molded containers by monitoring the sound adjacent predetermined location along the production line of plastic blow molded containers.
2. Description of the Prior Art
The leak testing of tanks, pressure vessels, and containers is an important manufacturing consideration in many different industries. In some instances, the gas-tight or liquid tight integrity of these components is usually determined by some form of a pressure-decay test. With this technique, the unit under test is injected with air to some specified overpressure, and the pressure is monitored for a specified period of time. If the pressure does not decay below a specified value at the end of the designated time period, the component under test is considered to be leak-free.
Another technique involves drawing a vacuum on the component being tested and then completely surrounding it with helium gas. A detector inside the vacuum system notifies the operator if helium is present in the air being pumped from the component.
Still another method involves the pressurization/immersion technique which consists of pressurizing the component, totally immersing the component in water or some other clear liquid, and observing the point of bubble emergence.
Yet another method utilizes a collimated beam of light which is scanned across the component under test. The test component has been pressurized with a tracer gas that strongly absorbs the light. When the light passes through the gas emerging from the source of the leak, the light energy absorbed by the gas produces an acoustic emission which is detected by a microphone. The resulting signal may be processed either as an alarm or it may be processed in coordination with the beam scanning mechanism to indicate exactly where the leak is located.
Another method involves apparatus adopted to detect the sound issued outwardly by the individual blow-molding dies during the blow-molding process wherein the sound is converted to an electrical signal and is compared with a reference signal or level and the faulty burst container is rejected.
Amongst the objectives of the present invention is to produce a method and apparatus for monitoring the production of blow molded plastic containers to detect the presence of a hole in the container during production of the containers.
Another object of the invention is to produce a method and apparatus that will detect the presence of a hole in a container being formed by a blow molding process.
Another object of the invention is to produce a method and apparatus for detecting a hole in the wall of a plastic container and producing a signal in response thereto.
The above as well as other objects of the invention may typically be achieved by a method and apparatus for monitoring the production of blow molded plastic containers comprising the steps of introducing pressure fluid to the interior of a plastic container being formed by a blow molding process;
acoustically sensing the sound of pressure fluid travelling through a hole in the plastic container being formed;
producing a control signal in response to the sound produced by the pressure fluid travelling through the hole in the plastic container; and
sensing the amplitude of the control signal to operatively identify the container with the hole.